Morality in Media has a bit of an issue with Groupon offering discounts to porn sites. From the release:

"Selling coupons supporting the degradation of women is as low as a publicly-traded company can go," said MIM executive director, Dawn Hawkins. "Groupon frames the tour as a historic one, comparing the opportunity to visiting the Smithsonian Institute because the building that houses Kink has an 'historic history in San Francisco.'"

Kink advertises that they have "young sexy teens who are overwhelmed and outnumbered...who need to learn a lesson by multiple men;" women being "bound, whipped, objectified and humiliated. They are immobilized, caged and humiliated as objects;" of women "suspended and tied in rope bondage...tormented beyond all reason;" and of women "naked, tied up, bound, punished, exposed in public...who are taken to public bars for public humiliation..."